1. Field of the Invention
The present invention relates to an etchant for etching at least one of a titanium material and silicon oxide, which is mainly used in a semiconductor process; and a method for fabricating a semiconductor device using such an etchant. As used herein, the term xe2x80x9ctitanium materialxe2x80x9d refers to both titanium and titanium oxide.
2. Description of the Related Art
Recently, titanium materials have been a target of attention as materials for a semiconductor device. Specifically, titanium has become increasingly important as a metal material usable for interconnects of a semi-conductor circuit or for silicifying metal. Ceramic materials containing titanium oxide has a high dielectric constant and thus is used for memories and capacitors in GaAs high-frequency integrated circuits. Recently, integrated circuits including a capacitor formed of a material having a high dielectric constant such as, for example, BaSrTiO3 or SrTiO3 have been actively developed.
Conventionally, conventional titanium materials are generally etched by ion milling. FIGS. 5A through 5E show a method for processing a material for a capacitor having a high dielectric constant by ion milling.
As shown in FIG. 5A, a lower electrode layer 2, a layer of a material used for a capacitor having a high dielectric constant (hereinafter, referred to as the xe2x80x9chigh dielectric constant capacitor material layerxe2x80x9d) 3, and an upper electrode layer 4 are sequentially formed on a substrate 1. As shown in FIG. 5B, a resist mask 5 is formed on the upper electrode layer 4. Then, as shown in FIG. 5C, the upper electrode layer 4 and the high dielectric constant capacitor material layer 3 are patterned by ion milling, thereby forming an upper electrode 4a. Standard conditions of ion milling include an accelerating voltage of 800 V and a beam current of 200 mA. Then, the resist mask 5 is removed. As shown in FIG. 5D, a resist mask 6 is formed on the lower electrode layer 2 so as to cover the high dielectric constant capacitor material layer 3 and the upper electrode 4a. The lower electrode layer 2 is patterned by ion milling as shown in FIG. 5E, thereby forming a lower electrode 2a. Then, the resist mask 6 is removed.
U.S. Pat. No. 4,759,823 discloses a two-step wet etching method used for PLZT. According to such a method, PLZT is immersed in a solution containing HCl and an F ion donor, and then immersed in nitric acid or acetic acid.
Ion milling which is performed for processing a titanium material can disadvantageously damage a semiconductor device due to Ar ions having a high energy. Ion milling has another problem of restricting the selection of the combination of the material to be milled and the material of an underlying layer. The wet etching method mentioned above also has the problem of significantly restricting the selection of the combination of the material to be etched and the material of an underlying layer formed of, for example, silicon oxide.
An etchant for etching at least one of a titanium material and silicon oxide includes a mixed liquid of HCl, NH4F and H2O.
In one embodiment of the invention, an etchant has a NH4F/HCl molar ratio of less than one.
In one embodiment of the invention, a method for fabricating a semiconductor device includes the step of etching a titanium material layer formed on a silicon oxide layer using such an etchant.
In one embodiment of the invention, an etchant has a NH4F/HCl molar ratio of more than one.
In one embodiment of the invention, a method for fabricating a semiconductor device includes the step of etching a silicon oxide layer formed on a titanium material layer using such an etchant.
In one embodiment of the invention, an etchant has a NH4F/HCl molar ratio of substantially one.
In one embodiment of the invention, a method for fabricating a semiconductor device includes the step of etching a lamination including a titanium material layer and a silicon oxide layer using such an etchant.
Thus, the invention described herein makes possible the advantages of providing an etchant for selectively etching either a titanium material or silicon oxide, or etching both a titanium material and silicon oxide at a substantially equal rate; and a method for fabricating a semiconductor device using such an etchant.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.